Decrease of seawater CO2 concentration in the Late Archean: An implication from 2.6 Ga seafloor hydrothermal alteration

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書誌事項

公開日
2013-10
権利情報
  • https://www.elsevier.com/tdm/userlicense/1.0/
  • https://www.elsevier.com/legal/tdmrep-license
DOI
  • 10.1016/j.precamres.2013.07.010
公開者
Elsevier BV

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説明

Abstract Before continents attained a critical aerial dimension on the early Earth, hydrothermal carbonation of subseafloor crust is considered to have played the dominant role in fixing CO 2 from the CO 2 -rich ocean. However, it is uncertain how and when the seawater CO 2 level decreased and the strong carbonation of oceanic crust ceased. Here we report the depth profiles of the volume concentration and the carbon isotopes of calcites in the Late Archean/Paleoproterozoic volcanic rocks (Fortescue and Hamersley groups), exposed in the southwestern Pilbara Craton, Western Australia. The depth profiles indicate that 2.6 Ga seafloor hydrothermal carbonation is well preserved in the study area and that the CO 2 content of subseafloor crust per seafloor unit area is estimated to be clearly lower than those in the Early and Middle Archean and similar to the Phanerozoic equivalents. This suggests that the CO 2 concentration in seawater decreased from the Middle Archean to the Late Archean. This period broadly corresponds to the time of the first appearance of supercontinent on Earth. The amalgamation of continents has the potential to decrease seawater CO 2 concentration due to the removal of platform carbonate to continental interior. Subsequent fragmentation of supercontinent likely cause the carbonate deposition around newly created continental shelves. It is therefore implied that seawater CO 2 concentration in the early Earth was lowered by not only the hydrothermal carbonation of subseafloor crust but also through the formation and breakup of supercontinent in the Late Archean.

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